TOP270 STARTUP PROBLEM
Dear Sirs,
I have designed an four-output PS based on TOP270EG device for universal input range (design based on your DER243). The PS starts and works normaly at 115V AC, but not (just momentarily/periodicaly)at 230V. Actually, the cold start is impossible until input capacitor is almost totaly discharged. Attached are the schematics as well as the transformer design sheet (prototype don by Dantrafo).
Best regards
Miroslav
Comments
Hi Wesley,
Thanks a lot for your engagement. I already disabled the secondary OVP (by removing R10 - 100R obtaining the perfect startup. I hope here is more matter of Zener voltage (bias winding voltage) rather then of the layout (I am still going to recheck it). The question is wether to increase the Zener voltage or decrease the bias winding turn number (by one).
Thanks for wire size recomendation too.
Best regards
Miroslav Sazdovski
You may be able to reduce the bias voltage, but before you do that you should check that this voltage does not go below 9V at no-load across your input range. This way you guarantee that you always supply enough energy to the IC. If you still have margin this will likely improve your standby power as well.
Regarding the layout you may want to check the application note for the IC you are using.
Hi Miroslav.
The first thing I suggest is to actually eliminate (for now) the OVP circuit. Simply ground the V pin. This will allow us to determine if the issue is coming from false triggering of the overvoltage protection. If this is the issue then you may need to review the zener diode you are using (maybe you need higher voltage), and double check that you don't have any noise coupling into your V pin (review your layout).
I took a look at your transformer and I noticed that you are using 0.8mm wire. I believe this wire will not provide you with any benefit because of skin effect. Typically I tend to stay at 0.45mm and use multiple wire strands if I have to.